Apparatus and method of cleaning a substrate

ABSTRACT

A cleaning apparatus is provided with a processing bath to be filled with a cleaning chemical, an ultrasonic oscillator, and a retainer for holding a substrate to be immersed into a cleaning chemical. The front surface of the substrate is cleaned while ultrasonic waves are radiated from the ultrasonic oscillator onto the back surface of the substrate.

FIELD OF THE INVENTION

The present invention relates to a method and apparatus for cleaning asubstrate, such as a semiconductor substrate.

BACKGROUND ART

When an interconnection pattern is formed on a semiconductor substrateduring the course of manufacture of a semiconductor device, a resistpattern is formed on a metal film; e.g., Al or Cu. The semiconductorsubstrate is subjected to plasma etching via the resist pattern, thusforming an interconnection pattern.

In association with an increase in the packing density of a device, asidewall protection film for protecting sidewalls of a pattern duringplasma etching is formed thickly, thus improving a geometry into whichthe metal film is to be etched. In this case, an altered resist layerresulting from plasma etching of a pattern, such as an Al or Cuinterconnection, tends to become more difficult to remove during aremoval process subsequent to the plasma etching process.

FIG. 7 is a conceptual drawing of a cross section of a pattern fordescribing the tendency. A resist layer 73 adhering to the side surfacesof an aluminum interconnection pattern 72 on a substrate 71 acts as asidewall protection film. Concurrently, an altered resist layer 75adheres also to the sidewalls of a resist pattern 74.

In order to eliminate the resist after etching, the altered resist layer75 has hitherto been removed by means of a wet etching method. However,there still remain residues of the altered layer that cannot be removedby the solubility of the resist in a chemical.

Alternatively, a single wafer processing cleaner has hitherto beenemployed. FIG. 8 is a conceptual drawing of an example of such aprocessing cleaner. In the cleaner, a substrate 82 to be cleaned isplaced on top of a rotary stage 81, and chemicals are dropped from achemical drop nozzle 83 onto the substrate 82. In the case of such arotary method, structural limitations are imposed on introduction ofultrasonic cleaner for improving the removal.

The present invention has been conceived to solve the drawbacks of therelated-art cleaning technology as described above. To this end, thereis adopted a dipping method of introducing a chemical into a processingbath. A substrate to be cleaned is immersed in the chemical and exposedto ultrasonic waves, thereby improving a cleaning effect and promotingremoval of an altered resist layer adhering to the substrate.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, a substrate cleaningapparatus comprises: a processing bath to be filled with a cleaningchemical, an ultrasonic oscillator disposed in the processing bath andimmersed in the cleaning chemical, and a retainer for retaining asubstrate to be immersed in the cleaning chemical such that ultrasonicwaves originating from the ultrasonic oscillator are radiated onto aback surface of the substrate.

In another aspect, the ultrasonic oscillator has a plurality ofoscillation sources disposed in a dispersed manner.

In another aspect, the substrate cleaning apparatus further comprises arotary mechanism for rotating the substrate retained by the retainer.

In another aspect, the substrate cleaning apparatus further comprisespropagation control apparatus for scattering or damping ultrasonic wavesoriginating from the ultrasonic oscillator.

In another aspect, in the substrate cleaning apparatus, the propagationcontrol apparatus is constituted by means of placing, in a propagationpath of ultrasonic waves, a plate-like member having a plurality ofopenings selectively formed therein.

In another aspect, the propagation control apparatus includes jetnozzles for squirting a chemical in the propagation path of ultrasonicwaves, thus circulating a flow of chemical.

According to another aspect of the present invention, in a substratecleaning method, a substrate whose surface has been processed isimmersed in a cleaning chemical filled in a processing bath, andultrasonic waves are radiated onto a back surface of the substrate,thereby cleaning a front surface of the substrate.

Other and further objects, features and advantages of the invention willappear more fully from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view schematically showing a configurationof a substrate cleaning apparatus according to a first embodiment of thepresent invention.

FIG. 2 depicts a preferred example of the ultrasonic oscillator, showingan example layout in which the radiators are arranged on the surface ofthe ultrasonic oscillator.

FIG. 3 is a cross-sectional view schematically showing a construction ofa substrate cleaning apparatus according to a second embodiment of thepresent invention.

FIG. 4 is a cross-sectional view schematically showing a construction ofa substrate cleaning apparatus according to a third embodiment of thepresent invention.

FIG. 5 is a plan view showing a preferred example of the shield plateadapted in the third embodiment.

FIG. 6 is a cross-sectional view schematically showing a construction ofa substrate cleaning apparatus according to a fourth embodiment of thepresent invention.

FIG. 7 is a conceptual drawing of a cross section of a pattern fordescribing an etching process.

FIG. 8 is a conceptual drawing of an example of a conventionalprocessing cleaner.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be described hereinbelow byreference to the accompanying drawings. Throughout the drawings, like orcorresponding elements are assigned identical reference numerals, andtheir repeated explanations are simplified or omitted.

First Embodiment

FIG. 1 is a cross-sectional view schematically showing a configurationof a substrate cleaning apparatus according to a first embodiment of thepresent invention.

In the cleaning apparatus shown in FIG. 1, a processing bath 1 (or achemical bath 1) is filled with a cleaning chemical 2. An ultrasonicoscillator 3 is disposed so as to be immersed in the cleaning chemical 2within the processing bath 1. Preferably, the ultrasonic oscillator 3 isdisposed in the vicinity of an interior bottom of the processing bath 1.A retainer 5 for holding a substrate 4 to be cleaned is disposed,preferably, in the vicinity of an interior upper portion of theprocessing bath 1 such that the substrate 4 is immersed and held in thecleaning chemical 2.

Radiators 31 (or oscillators 31), which serve as radiation sources foremitting ultrasonic waves, are provided on the surface of the ultrasonicoscillator 3. The surface of each of the radiators 31 is oriented towardthe substrate 4. The radiators 31 are dispersed at appropriate intervalson the surface of the ultrasonic oscillator 3. The ultrasonic oscillator3 is constituted by means of housing the ultrasonic radiators 31 into,e.g., a chemical-resistant box.

FIG. 2 depicts a preferred example of the ultrasonic oscillator 3,showing an example layout in which the radiators 31 are arranged on thesurface of the ultrasonic oscillator 3. Each of the radiators 31 has adiameter of, e.g., about 1.5 cm, and the radiators 31 are affixed to asurface plate 32 in a uniformly-dispersed manner at an interval of about5 cm.

Ultrasonic waves are emitted from the radiators 31 by means ofactivation of the ultrasonic oscillator 3. The ultrasonic wavespropagate through the chemical 2 and are irradiated onto the backsurface of the substrate 4. As a result, removal of an altered resistlayer adhering to the front surface of the substrate 4 is promoted. Forthis reason, as shown in FIG. 2, a plurality of radiators 31 arepreferably arranged at small intervals in a dispersed manner, therebyimproving the consistency of radiated ultrasonic waves within a plane.On the contrary, if one radiator 31 or only a small number of radiators31 would be provided, an undesirable difference will arise between onearea of the substrate 4 located immediately above the radiators 31 andthe other area surrounding the one area of the substrate 4, in terms ofintensity of ultrasonic waves radiated onto the back surface of thesubstrate 4.

As has been described above, in the present embodiment, the processingbath 1 filled with a cleaning chemical is provided with the ultrasonicoscillator 3 and the retainer 5 for holding the substrate 4 to beimmersed into the cleaning chemical 2 for cleaning purpose. Ultrasonicwaves originating from the ultrasonic oscillator 3 are radiated onto theback surface of the substrate 4, thereby cleaning the front surface ofthe substrate 4.

Use of such a method promotes removal of an altered resist layer orresist residues adhering to the front surface of the substrate 4; forexample, an altered resist layer or resist residues resulting fromplasma etching of a pattern, such as an Al pattern or a Cu pattern.

Second Embodiment

FIG. 3 is a cross-sectional view schematically showing a construction ofa substrate cleaning apparatus according to a second embodiment of thepresent invention.

In this embodiment, in addition to the structure of a cleaning apparatusshown in FIG. 1, the cleaning apparatus shown in FIG. 3 is furtherprovided with a rotary mechanism 6 for rotating the retainer 5 thatholds the substrate 4. For instance, the rotary mechanism 6 rotates theretainer 5 at a constant speed in a circumferential direction whilesupporting the retainer 5 from below. As a result, the substrate 4 canbe rotated in the circumferential direction while remaining within thechemical.

As a result, the surface of the substrate 4 is cleaned with thechemical, thereby improving a cleaning effect. Further, even ifinconsistency exists in the intensity profile of ultrasonic wavesradiated onto the substrate 4, oscillation exerted within the plane ofthe substrate 4 can be made consistent by means of rotating thesubstrate 4. Thus, the effect of ultrasonic waves can be averaged,thereby improving a cleaning effect.

Third Embodiment

FIG. 4 is a cross-sectional view schematically showing a construction ofa substrate cleaning apparatus according to a third embodiment of thepresent invention.

In addition to the structure of the cleaning apparatus shown in FIG. 1,the cleaning apparatus shown in FIG. 4 is further provided with a shieldplate 7 disposed between the ultrasonic oscillator 3 and the substrate 4within the processing bath 1; in short, in a path along which ultrasonicwaves propagate. The shield plate 7 can scatter or attenuate ultrasonicwaves. Specifically, the shield plate 7 is an example of a propagationcontrol member for controlling a propagation characteristic ofultrasonic waves. For example, a member of mesh structure is utilized asthe shield plate 7.

As has already been mentioned, utilization of ultrasonic waves forcleaning the substrate 4 promotes removal of an altered resist layeradhering to the substrate 4. There may be a case where there is anecessity of controlling the intensity of ultrasonic waves so as not toimpose damage (e.g., exfoliation or corrosion) to Al or Cu, which servesa material of the interconnection, formed on the substrate 4. In thiscase, there is selected a shield plate 7 having an appropriate shieldingeffect, and the thus-selected shield plate 7 is disposed, therebycontrolling influence of ultrasonic waves.

When the profile of consistency of ultrasonic waves radiated onto thesubstrate 4 is not necessarily sufficient, a shield plate is interposedbetween the ultrasonic oscillator 3 and the substrate 4, therebyoptimizing the ultrasonic waves through scattering and attenuation.

FIG. 5 is a plan view showing a preferred example of the shield plate 7.The shield plate 7 is formed, by means of forming in a plate member 71 aplurality of slits 72 of appropriate width at predetermined intervals.For instance, a stainless plate or another metal plate possessingchemical resistance can be utilized as the plate member 71. Preferably,a material that does not absorb ultrasonic waves is used. The width ofthe slit 72 is set to, e.g., 1 to 2 cm. Ultrasonic waves passing throughthe slits 72 can be controlled by means of adjusting an area ratio ofthe slits 72 to the shield plate 7. Thus, the intensity of ultrasonicwaves propagating through the shield plate 7 can be controlled.

As another example of the shield plate 7, shield plates 7 shown in FIG.5 are stacked into a double layer, and the positions of the shieldplates 7 are displaced from each other through adjustment. As a result,the area ratio of the slits 72 to the stacked shield plates 7 can bevariably adjusted.

The shield plate 7 possesses chemical resistance, and is made ofmaterial which does not absorb ultrasonic waves. By means of variablychanging the area ratio of the slits 72 to the shield plate or plates 7,required action of ultrasonic waves can be selected for each substrate4.

Fourth Embodiment

FIG. 6 is a cross-sectional view schematically showing a construction ofa substrate cleaning apparatus according to a fourth embodiment of thepresent invention.

In addition to the construction of the cleaning apparatus shown in FIG.1, the cleaning apparatus shown in FIG. 6 is further provided with jetnozzles 8 disposed between the ultrasonic oscillator 3 and the substrate4 beside a path along which ultrasonic waves propagate to the substrate4. The jet nozzles 8 squirt the chemical 2 toward the propagation pathof ultrasonic waves. A plurality of jet nozzles 8 are provided in thevicinity of an interior wall of the processing bath 1. The jet nozzles 8are one example of propagation control members for controlling thepropagation characteristic of ultrasonic waves.

Jet flows 21 of the chemical 2 are induced by the jet nozzles 8, therebystirring or agitating a chemical located in the propagation path ofultrasonic waves, to thereby adjust the flow of chemical within theprocessing bath 1. As a result, linear radiation of ultrasonic waves isscattered, and the consistency of radiation of ultrasonic waves due tostirring effect can be improved. Further, the stirring effect cancontribute to lessening of damage which arises on the surface of thesubstrate 4.

During manufacture of a semiconductor device, a substrate is cleanedthrough use of the substrate cleaning method or apparatus described inconnection with the previous embodiments, thereby, enabling manufactureof a semiconductor device. A cleaning process can be made efficient.

In each of the embodiments, the present invention has been described bymeans of taking a semiconductor substrate or a semiconductor device asan example. However, the substrate is not limited to a semiconductorsubstrate; the present invention can be applied to a substrate ofanother electronic device in the same manner. Products to bemanufactured finally are not limited to semiconductor devices and may beother electronic devices.

The features and the advantages of the present invention may besummarized as follows.

Under the substrate cleaning apparatus and method according to thepresent invention, a substrate is cleaned within a cleaning chemicalwhile being exposed to ultrasonic waves, thus improving an effect ofcleaning a substrate.

Under the substrate apparatus and method according to the presentinvention, a substrate to be cleaned is cleaned while being rotatedwithin a chemical, thus yielding an effect of rendering a cleaningeffect uniform within a plane of the substrate.

Under the substrate apparatus and method according to the presentinvention, the intensity of ultrasonic waves to be radiated onto asubstrate to be cleaned is adjusted, or a distribution profile ofultrasonic waves is made uniform. As a result, a cleaning effectachieved within a plane of a substrate to be cleaned can be controlled,and the cleaning effects can be made uniform.

Under the substrate apparatus and method according to the presentinvention, a substrate is cleaned while being subjected to radiation ofultrasonic waves with a cleaning chemical that is being stirred oragitated. Hence, the consistency of radiation of ultrasonic waves isimproved, thereby controlling an effect of cleaning a substrate orrendering the cleaning effect uniform. It is further understood that theforegoing descriptions are preferred embodiments of the disclosedapparatus and that various changes and modifications may be made in theion without departing from the spirit and scope thereof.

The entire disclosure of a Japanese Patent Application No. 2001-016964filed on Jan. 25, 2001 including specification, claims, drawings andsummary, on which the Convention priority of the present application isbased, are incorporated herein by reference in its entirety.

1. A substrate cleaning method characterized in that a substrate whosesurface has been processed is immersed in a cleaning chemical filled ina processing bath, and ultrasonic waves are radiated onto a back surfaceof the substrate, thereby cleaning a front surface of the substrate. 2.The substrate cleaning method according to claim 1, wherein ultrasonicwaves originate from a plurality of origination sources disposed in adispersed manner.
 3. The substrate cleaning method according to claim 1,wherein the substrate is cleaned while being rotated.
 4. The substratecleaning method according to claim 1, wherein ultrasonic waves areradiated by way of a propagation control member for scattering ordamping ultrasonic waves.
 5. The substrate cleaning method according toclaim 1, wherein cleaning is effected while the chemical through whichultrasonic waves propagate is stirred or agitated.
 6. A method ofmanufacturing a semiconductor device through use of the substratecleaning method defined in claim 1.